This invention relates to an apparatus for repairing defects in a mask, which is used in semiconductor manufacture, by using an ion beam, and more particularly relates to an ion beam regulating apparatus for obtaining a suitable spot shape of a focused ion beam.
A conventional method of focusing and correcting astigmatic ion beams is as follows.
The intensity of secondary ions which are generated in the surface of a pattern when a sample is scanned with a focused ion beam is detected by a detector. A signal representative of the detected intensity is introduced as a picture signal into a picture display unit so as to observe an image of the pattern. Since the spot shape 1 of this ion beam on the surface of the sample has a predetermined area, an end region 3 of the image obtained of the pattern 2 is not clear, and the brightness of the end region 3 varies continuously in accordance with variations in the diameter of the ion beam spot as shown in FIG. 2. The diameter of the ion beam spot is regulated as this region of varying brightness of the image is observed.
In a conventional ion beam regulating method, a beam spot is regulated according to an end region, the brightness of which varies continuously, of a pattern observed with the naked eye, so that the beam spot cannot be accurately regulated. Also regulating this beam spot requires great skill.